Brown’s campaign has launched this latest TV spot amid controversy over the racist behavior of his sophomoric supporters and staff members, who mocked Warren’s claims of Native American heritage with ­tomahawk chops and war whoops last weekend. Classy. Rather than backing away from that behavior, Brown has rushed back ­toward the issue that gave rise to it.

In the new ad, people on the street make not-very-spontaneous assertions about ­Warren having been caught in a lie over her heritage, though I watched it a few times and none of them seem clear on what the actual lie was.

For those of you who have been living in a box (according to a Globe poll released Sunday, only 11 percent of likely voters are not at all familiar with this controversy), Brown has been hammering Warren for months for listing herself as Native American in a law school directory. After fumbling and ducking, ­Warren eventually explained that she identified herself as a minority because she grew up being told she had Native American ancestry. Whether or not she was right to do this, ­Warren says she never got a job or promotion because of it. And not a single person at the colleges that employed her has challenged that assertion.

But none of that matters to Brown, who continues to assert, without evidence, that Warren claimed minority status falsely and for career gain. Their first debate had barely begun when the senator did an uncannily lifelike impression of ignorance: “Professor ­Warren claimed that she was a Native American, a person of color,” Brown said. “And, as you can see,” he continued, waving a hand in her direction, “she’s not.”

Yeah, because in 2012 it’s totally cool to point at somebody and say he or she can’t be a minority because they don’t look like one. (Close observers will see a clue here as to why Brown feels no need to fire staff members for their boorish behavior).

Look, Warren’s family told her that she had Cherokee and Delaware ancestors and that her parents eloped because his father’s family didn’t want him marrying a woman with ­Native American blood. In an exhaustively ­reported story, the Globe’s Sally Jacobs found evidence of the elopement, and some Warren relatives – including a second cousin who had no idea Warren was running for office – who were told the same stories about their ancestry. If I’d grown up with those stories, I’d ­believe I had Native American heritage, too — just as my stories convince my fair child that he has Lebanese heritage. Why on earth would he think otherwise?

There are real issues at stake in this election. Where our US Senator stands on unemployment, the widening gap between the rich and the rest of us, abortion rights, and Medicare’s future really affects our lives. Yet the Brown campaign appears utterly fixated on accusations for which the Washington Post’s Fact Checker gives them Two Pinocchios.

So why does Brown persist? Well, here’s the most demoralizing part of the whole mess: It works. Back in March, when asked for a word to describe Warren, 1 percent of ­respondents to a Globe poll said “dishonest.” In the survey completed last week, that number jumped to 12 percent.

According to the Globe poll, 18 percent of voters are still undecided in this race, and 19 percent of that group are less likely to vote for Warren because of the Native American flap. That amounts to 3 percent of voters overall who could break Brown’s way if he keeps hammering the issue. He clearly believes that sliver of the electorate is worth the potential for racist outbursts and for damage to his nice-guy image.

Maybe if I had little else to offer those voters, I’d take that risk, too.

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